1. Field of the Invention
The present invention relates to an insulated bobbin for a stator in a multipolar magneto used as an electrical component in the engine of a two-wheeled vehicle, a snowmobile, outboard equipment, a buggy, a water-bike and the like.
2. Description of the Related Art
FIG. 12 is a partially sectional side view of a conventional multipolar magneto as disclosed, for instance, in Japanese Unexamined Utility Model Publication No. 58-124051. Furthermore, FIG. 13 is a front view of a multipolar magneto. Furthermore, FIG. 14 is a perspective view of an insulated bobbin for a stator of a conventional multipolar magneto. In FIG. 12 and FIG. 13, a tapered portion is provided to the center of a center piece 41 and is fitted to the crankshaft of an engine. A fly wheel 43 is molded from an iron plate and is fixed to a flange 42 of the center piece 41 by a rivet 44.
Then, magnets 45 and non-magnetic support plates 46 are attached to the inner rim of the fly wheel 43, the magnets 45 being provided in the perimeter direction with alternately different polarities. On the inner side of the magnets 45, a stator 50 is fixed so as to face the inner side with a gap therebetween. The stator 50 has the following constitution.
As shown in FIG. 14, a stator iron core 1 has multiple projecting poles 1b extending radially, the projecting poles 1b being formed by lamination of multiple thin iron layers. As shown in FIG. 12 and FIG. 13, generator coil 3 is wound around the projecting poles 1b, and these are electrically connected to form a generator circuit. Insulated bobbins 52 are made from resin and are fitted into the wire-winding portions of the projecting poles 1b. Each insulated bobbin 52 is divided into a first bobbin 53 and a second bobbin 54, which clasp the projecting pole 1b from each side with respect to the lamination direction of the stator iron core 1.
FIG. 15 is a front view of another example of an insulated bobbin for stator in a conventional multipolar magneto, illustrating the bobbin of one side only. FIG. 16 is an underside view of a bobbin. Furthermore, FIG. 17 shows a front view of parts corresponding to one projecting pole 1b and a view of these parts from the inner side of the bobbin, and FIG. 18 shows an underside view of parts corresponding to one projecting pole 1b and a view of these parts from the outside of the bobbin and from the side. On the other hand, FIG. 19 is a cross-sectional view taken along the line XIX--XIX of FIG. 16 and FIG. 17. Furthermore, FIG. 20 is a cross-sectional view and a partially enlarged cross-sectional view taken along the line XX--XX of FIG. 16.
In FIG. 15-FIG. 18, the insulated bobbin for stator is divided into two bobbins of identical shape. Below, only a first bobbin 61 of one side will be explained. Firstly, the bobbin 61 has a substantially cylindrical bobbin inner rim wall 61a. Then, a projection 61b, which is U-shaped in cross-section, projects radially from the bobbin inner rim wall 61a in the diameter direction. The projection 61b has a pair of side walls 61c and 61d which extend along both side faces of the projecting pole 1b of the core 1. A brim 61e is provided at the tip of the projection 61b and spreads along the flange of the core 1.
Furthermore, as shown clearly in FIG. 19, the pair of side walls 61c and 61d of the projection 61b are the same height. Therefore, the edges of the opening side of the cross-sectional U-shape of the projection 61b form a single face. Furthermore, the pair of side walls 61c and 61d are provided so as to form parallel faces.
In addition, as shown clearly in FIG. 20, the tip edges of the side walls 61c and 61d of the projection 61b are molded to form a rectangle having right-angled corners.
In the insulated bobbin for stator of the above constitution, the first bobbin 61 and a second bobbin (not shown in the diagram) having the same shape as the first bobbin 61 are provided, and the first bobbin 61 and the second bobbin are arranged so as to clasp the projecting pole 1b of the stator iron core 1 from above and below with respect to the lamination direction. Thereafter, a generator coil is attached by winding. Then, the insulated bobbin provides electrical insulation between the stator iron core 1 and the generator coil 3.
In the insulated bobbin for stator of such a constitution, firstly, since the portion which the projecting pole 1b of the stator iron core 1 is inserted into, that is, the edges of the cross-sectionally U-shaped projection 61b, are the same height and in a single plane, when the stator iron core 1 is inserted into the insulated bobbin, positioning is awkward and insertion is difficult.
Furthermore, since the edges have not been chamfered, the corners of the edges strike the stator iron core 1, making it difficult to insert the stator iron core 1 into the insulated bobbin.
Furthermore, as shown in FIG. 21, in the conventional insulated bobbin, heat shrinkage after molding causes the insides of the side walls 61c and 61d of the projection 61b to warp into an arc. Moreover, as shown in FIG. 22, in the conventional insulated bobbin, this deformation makes the opening side of the projection 61b narrow. As a result of such deformation, insertability of the stator iron core 1 is extremely poor.
On the other hand, when the thickness of the bobbin is increased in order to prevent deformation due to heat shrinkage after the insulated bobbin has been molded, there is less space for winding coil, consequently reducing output characteristics. In addition, when the thickness of the bobbin is increased, the coil has poor heat radiation, consequently raising the temperature of the generator coil 3.
Furthermore, when the gap between the stator iron core 1 and the bobbin is increased to enable the bobbin to fit around the stator iron core 1 even when the bobbin has suffered deformation due to heat shrinkage after molding, space for coil winding is reduced and output characteristics deteriorate. Furthermore, since the bobbin and the stator iron core 1 do not closely contact each other, when winding coil, there is a possibility that the bobbin may break due to tension of the conductive wire, or that the bobbin may move during winding and consequently disturb the winding of the wire.
In addition, in the conventional insulated bobbin for stator, after coil has been wound, the coil is secured by impregnation of varnish. However, since the open-end wire of the coil is not fixed before applying the varnish, the coil slackens during application of the varnish so that the coil is secured in a floating state, reducing vibration resistance of the coil.
Furthermore, an insulated bobbin for stator generally comprises resin mixed with glass fabric, and conventionally, high-tenacity nylon or the like is mainly used as the resin in order to prevent breakage. However, nylon has a disadvantage of poor insulation characteristics at high temperatures.